Chemical shift index
The chemical shift index or CSI is a widely employed technique in biomolecular NMR spectroscopy that can be used to display and identify the type, location and extent of protein secondary structures (helices, beta strands and random coil regions) using only backbone chemical shift information . Originally developed in 1992 for interpreting 1Hα chemical shifts, the chemical shift index exploits the well known tendency of 1Hα shifts to be shifted upfield (towards the right side of a NMR spectrum) of their random coil values in helices and downfield (towards the left side of a NMR spectrum) of their random coil values in beta strands.